Uranus' Moon Titania - Universe Today Universe Today by Matt Williams Like all of the Solar Systems’ gas giants, Uranus has an extensive system of moons. In fact, astronomers can now account for 27 moons in orbit around Uranus. Of these, none are greater in size, mass, or surface area than Titania. One of the first moon’s to be discovered around Uranus, this heavily cratered and scarred moon was appropriately named after the fictional Queen of the Fairies. Discovery and Naming: Titania was discovered by William Herschel on January 11th, 1787, the English astronomer who had discovered Uranus in 1781. The discovery was also made on the same day that he discovered Oberon , Uranus’ second-largest moon. Although Herschel reported observing four other moons at the time, the Royal Astronomical Society would later determine that this claim was spurious. It would be almost five decades after Titania and Oberon was discovered that an astronomer other than Herschel would observe them.

In addition, Titania would be referred to as “the first satellite of Uranus” for many years – or by the designation Uranus I, which was given to it by William Lassell in 1848. By 1851, Lassell began to number all four known satellites in order of their distance from the planet by Roman numerals, at which point Titania’s designation became Uranus III. By 1852, Herschel’s son John, and at the behest of Lassell himself, suggested the moon’s name be changed to Titania, the Queen of the Fairies in A Midsummer Night’s Dream. This was consistent with all of Uranus’ satellites, which were given names from the works of William Shakespeare and Alexander Pope. A montage of Uranus’s moons. Image credit: NASA Size, Mass and Orbit: With a diameter of 1,578 kilometers, a surface area of 7,820,000 km² and a mass of 3.527±0.09 × 1021 kg, Titania is the largest of Uranus’ moons and the eighth largest moon in the Solar System.

At a distance of about 436,000 km (271,000 mi), Titania is also the second farthest from the planet of the five major moons. Titania’s moon also has a small eccentricity and is inclined very little relative to the equator of Uranus. It’s orbital period, which is 8.7 days, is also coincident with it’s rotational period. This means that Titania is a synchronous (or tidally-locked) satellite, with one face always pointing towards Uranus at all times. Because Uranus orbits the Sun on its side, and its moons orbit the planet’s equatorial plane, they are all subject to an extreme seasonal cycle, where the northern and southern poles experience 42 years of either complete darkness or complete sunlight. Composition: Scientists believe Titania is composed of equal parts rock (which may include carbonaceous materials and organic compounds) and ice. This is supported by examinations that indicate that Titania has an unusually high-density for a Uranian satellite (1.71 g/cm³).

The presence of water ice is supported by infrared spectroscopic observations made in 2001–2005, which have revealed crystalline water ice on the surface of the moon. Uranus and its five major moons, with Titania being the farthest left. Credit: space.com It is also believed that Titania is differentiated into a rocky core surrounded by an icy mantle. If true, this would mean that the core’s radius is approx. 520 km (320 mi), which would mean the core accounts for 66% of the radius of the moon, and 58% of its mass. As with Uranus’ other major moons, the current state of the icy mantle is unknown. However, if the ice contains enough ammonia or other antifreeze, Titania may have a liquid ocean layer at the core-mantle boundary. The thickness of this ocean, if it exists, is up to 50 km (31 mi) and its temperature is around 190 K. Naturally, it is unlikely that such an ocean could support life. But assuming this ocean supports hydrothermal vents on its floor, it is possible life could exist in small patches close to the core.

However, the internal structure of Oberon depends heavily on its thermal history, which is poorly known at present. Voyager 2: The only direct observations made of Titania were conducted by the Voyager 2 space probe, which photographed the moon during its flyby of Uranus in January 1986. These images covered about 40% of the surface, but only 24% was photographed with the precision required for geological mapping. Voyager’s flyby of Titania coincided with the southern hemisphere’s summer solstice, when nearly the entire northern hemisphere was unilluminated. As with the other major moon’s of Uranus, this prevented the surface from being mapped in any detail. No other spacecraft has visited the Uranian system or Titania before or since, and no mission is planned in the foreseeable future. Interesting Facts: Titania is intermediate in terms of brightness, occupying a middle spot between the dark moons of Oberon and Umbriel and the bright moons of Ariel and Miranda . It’s surface is generally red in color (less so than Oberon), except where fresh impact have taken place, which have left the surface blue in color.

The surface of Titania is less heavily cratered than the surface of either Oberon or Umbriel, suggesting that its surface is much younger. Like all of Uranus’ major moons, it’s geology is influenced by a combination of impact craters and endogenic resurfacing. Whereas the former acted over the moon’s entire history and influenced all its surfaces, the latter processes were mainly active following the moon’s formation and resulted in a smoothing out of its features – hence the low number of present-day impact craters. Overall, scientists have recognized three classes of geological feature on Titania. These include craters, faults (or scarps) and what are known as grabens (sometimes called canyons). Titania’s craters range in diameter from a few kilometers to 326 kilometers – in the case of the largest known crater, Gertrude . Titania’s surface is also intersected by a system of enormous faults (scarps); and in some places, two parallel scarps mark depressions in the satellite’s crust, forming grabens (aka. canyons).

The grabens on Titania range in diameter from 20 to 50 kilometers (12–31 mi) and in a relief (i.e. depth) from 2 to 5 km. The most prominent graben on Titania is the Messina Chasma, which runs for about 1,500 kilometers (930 mi) from the equator almost to the south pole. The grabens are probably the youngest geological features on Titania, since they cut through all craters and even the smooth plains. Voyager 2’s highest-resolution image of Titania, showing cratered plains, enormous rifts and long scarps. Near the bottom, the crater Ursula is split by the graben Belmont Chasma. Credit: NASA Like Oberon, the surface features on Titania have been named after characters in works by Shakespeare, with all of the physical features are named after female characters. For instance, the crater Gertrude is named after Hamlet’s mother, while other craters – Ursula, Jessica, and Imogen – are named after characters from Much Ado About Nothing, The Merchant of Venice, and Cymebline, respectively.

Interestingly, the presence of carbon dioxide on the surface suggests that Titania may also have a tenuous seasonal atmosphere of CO², much like that of the Jovian moon Callisto . Other gases, like nitrogen or methane, are unlikely to be present, because Titania’s weak gravity could not prevent them from escaping into space. Like all of Uranus’ moons, much remains to be discovered about this most-massive of her satellites. In the coming years, one can only hope that NASA, the ESA, or other space agencies decide that another Voyager-like mission is need to the outer Solar System. Until such time, Uranus and the many moons that orbit it will continue to keep secrets from us. You should also check out Titania and the moon Titania . Astronomy Cast has an episode on William Herschel you will find interesting. Reference: Uranus' moon Titania Uranus' moon Titania July 6, 2015 by Matt Williams, Universe Today Voyager 2 image of Titania, Uranus’ largest moon. Credit: NASA Like all of the Solar Systems' gas giants, Uranus has an extensive system of moons.

In fact, astronomers can now account for 27 moons in orbit around Uranus. Of these, none are greater in size, mass, or surface area than Titania. One of the first moon's to be discovered around Uranus, this heavily cratered and scarred moon was appropriately named after the fictional Queen of the Fairies. Discovery and Naming: Titania was discovered by William Herschel on January 11th, 1787, the English astronomer who had discovered Uranus in 1781. The discovery was also made on the same day that he discovered Oberon, Uranus' second-largest moon . Although Herschel reported observing four other moons at the time, the Royal Astronomical Society would later determine that this claim was spurious. It would be almost five decades after Titania and Oberon was discovered that an astronomer other than Herschel would observe them. In addition, Titania would be referred to as "the first satellite of Uranus" for many years – or by the designation Uranus I, which was given to it by William Lassell in 1848.

By 1851, Lassell began to number all four known satellites in order of their distance from the planet by Roman numerals, at which point Titania's designation became Uranus III. By 1852, Herschel's son John, and at the behest of Lassell himself, suggested the moon's name be changed to Titania, the Queen of the Fairies in A Midsummer Night's Dream. This was consistent with all of Uranus' satellites, which were given names from the works of William Shakespeare and Alexander Pope. Size, Mass and Orbit: With a diameter of 1,578 kilometers, a surface area of 7,820,000 km² and a mass of 3.527±0.09 × 1021 kg, Titania is the largest of Uranus' moons and the eighth largest moon in the Solar System. At a distance of about 436,000 km (271,000 mi), Titania is also the second farthest from the planet of the five major moons.

Titania's moon also has a small eccentricity and is inclined very little relative to the equator of Uranus. It's orbital period, which is 8.7 days, is also coincident with it's rotational period. This means that Titania is a synchronous (or tidally-locked) satellite, with one face always pointing towards Uranus at all times. Because Uranus orbits the Sun on its side, and its moons orbit the planet's equatorial plane, they are all subject to an extreme seasonal cycle, where the northern and southern poles experience 42 years of either complete darkness or complete sunlight. Composition: A montage of Uranus’s moons. Credit: NASA Scientists believe Titania is composed of equal parts rock (which may include carbaceous materials and organic compounds) and ice. This is supported by examinations that indicate that Titania has an unusually high-density for a Uranian satellite (1.71 g/cm³). The presence of water ice is supported by infrared spectroscopic observations made in 2001–2005, which have revealed crystalline water ice on the surface of the moon. It is also believed that Titania is differentiated into a rocky core surrounded by an icy mantle.

If true, this would mean that the core's radius is approx. 520 km (320 mi), which would mean the core accounts for 66% of the radius of the moon, and 58% of its mass. As with Uranus' other major moons, the current state of the icy mantle is unknown. However, if the ice contains enough ammonia or other antifreeze, Titania may have a liquid ocean layer at the core-mantle boundary. The thickness of this ocean, if it exists, is up to 50 km (31 mi) and its temperature is around 190 K. Naturally, it is unlikely that such an ocean could support life. But assuming this ocean supports hydrothermal vents on its floor, it is possible life could exist in small patches close to the core. However, the internal structure of Oberon depends heavily on its thermal history, which is poorly known at present. Voyager 2: The only direct observations made of Titania were conducted by the Voyager 2 space probe, which photographed the moon during its flyby of Uranus in January 1986.

These images covered about 40% of the surface, but only 24% was photographed with the precision required for geological mapping. Voyager's flyby of Titania coincided with the southern hemisphere's summer solstice, when nearly the entire northern hemisphere was unilluminated. As with the other major moon's of Uranus, this prevented the surface from being mapped in any detail. No other spacecraft has visited the Uranian system or Titania before or since, and no mission is planned in the foreseeable future. Uranus and its five major moons, with Titania being the farthest left. Credit: space.com Interesting Facts: Titania is intermediate in terms of brightness, occupying a middle spot between the dark moons of Oberon and Umbriel and the bright moons of Ariel and Miranda. It's surface is generally red in color (less so than Oberon), except where fresh impact have taken place, which have left the surface blue in color. The surface of Titania is less heavily cratered than the surface of either Oberon or Umbriel, suggesting that its surface is much younger. Like all of Uranus' major moons, it's geology is influenced by a combination of impact craters and endogenic resurfacing.

Whereas the former acted over the moon's entire history and influenced all its surfaces, the latter processes were mainly active following the moon's formation and resulted in a smoothing out of its features – hence the low number of present-day impact craters. Overall, scientists have recognized three classes of geological feature on Titania. These include craters, faults (or scarps) and what are known as grabens (sometimes called canyons). Titania's craters range in diameter from a few kilometers to 326 kilometers – in the case of the largest known crater, Gertrude. Titania's surface is also intersected by a system of enormous faults (scarps); and in some places, two parallel scarps mark depressions in the satellite's crust, forming grabens (aka. canyons). The grabens on Titania range in diameter from 20 to 50 kilometers (12–31 mi) and in a relief (i.e. depth) from 2 to 5 km. The most prominent graben on Titania is the Messina Chasma, which runs for about 1,500 kilometers (930 mi) from the equator almost to the south pole.

The grabens are probably the youngest geological features on Titania, since they cut through all craters and even the smooth plains. The video will load shortly Like Oberon, the surface features on Titania have been named after characters in works by Shakespeare, with all of the physical features are named after female characters. For instance, the crater Gertrude is named after Hamlet's mother, while other craters – Ursula, Jessica, and Imogen – are named after characters from Much Ado About Nothing, The Merchant of Venice, and Cymebline, respectively. Interestingly, the presence of carbon dioxide on the surface suggests that Titania may also have a tenuous seasonal atmosphere of CO², much like that of the Jovian moon Callisto. Other gases, like nitrogen or methane, are unlikely to be present, because Titania's weak gravity could not prevent them from escaping into space. Like all of Uranus' moons, much remains to be discovered about this most-massive of her satellites. In the coming years, one can only hope that NASA, the ESA, or other space agencies decide that another Voyager-like mission is need to the outer Solar System.

Until such time, Uranus and the many moons that orbit it will continue to keep secrets from us. Voyager 2’s highest-resolution image of Titania, showing cratered plains, enormous rifts and long scarps. Near the bottom, the crater Ursula is split by the graben Belmont Chasma. Credit: NASA Titania, moon of Uranus - The Solar System on Sea and Sky (NASA/JPL) Queen of the Fairies Titania [Ty-TAY-ne-ah] is the fourteenth of Uranus' moons and is the largest. Although it is the largest moon of Uranus, it is much smaller than Triton, the largest moon of Uranus' sister planet, Neptune. It was named after the Queen of the Fairies and wife of Oberon in Shakespeare's Midsummer-Night's Dream. Titania was discovered in 1787 by Sir William Herschel, who also discovered Uranus and Oberon. Most of what we know about Titania was learned from the mission of Voyager 2 when it flew past the moon in 1986. A Large, Dirty Ice Ball Titania is believed to be composed of about half water ice and half rocky material.

It is very similar in composition to Ariel, but is much larger. It is also similar to Saturn's moon, Rhea, although it contains a greater percentage of rock. Some astronomers have referred to these moons as "dirty ice balls" because they resemble a ball of ice mixed with dirt and rock. The surface of Titania is littered with impact craters. Many of these craters are surrounded by brightly colored ejecta material. This material was thrown out onto the moon's surface by the impacts that formed the craters. Features of Titania Surface features on Titania range from impact craters to rift valleys and faults. There are a few large impact basins on the surface, but most of the craters are small. A large, double-walled crater is located near the top of the moon. Many of the craters on Titania appear to be partially submerged. This would seem to indicate that the surface is relatively young, and has resurfaced itself at some point in the recent past. Several interconnecting rift valleys can be seen crossing the moon's surface. These are similar to the valleys on Ariel except that they are not quite as extensive. One of these valleys is 1000 miles (1600 km) in length.

Several faults also exist on Titania's surface. This indicated that the moon was probably geologically active at some time in the distant past. Some astronomers believe that Titania's surface may have cooled before its interior. When the interior began to cool, it expanded and formed the rift valleys and faults that are visible today. Titania has no atmosphere and no magnetic field. Oberon Oberon Oberon ("OH buh ron") is the outermost of Uranus ' large satellites and the second largest: orbit : 583,420 km from Uranus diameter : 1523 km mass : 3.03e21 kg Oberon is the King of the Fairies and husband of Titania in Shakespeare's Midsummer-Night's Dream. Discovered by Herschel in 1787. Oberon and Umbriel appear quite similar though Oberon is 35% larger. All of Uranus' large moons are a mixture of about 40-50% water ice with the rest rock, a somewhat larger fraction of rock than Saturn 's large moons such as Rhea . Oberon's heavily cratered surface has probably been stable since its formation.

It has far more and larger craters than do Ariel and Titania . Some of the craters have rays of ejecta similar to those seen on Callisto . Some of the crater floors are dark, perhaps covered with darker material (dirty water?) that upwelled into the crater. Large faults are also seen across the entire southern hemisphere of Oberon. This indicates some geologic activity early in Oberon's history. The picture above shows a mountain on the limb that rises 6 km above its surrounds. It is actually possible to see Uranus's 4 largest moons with an amateur telescope. But it takes a very dark sky and a telescope with at least a 12 inch (30 cm) aperture. More about Oberon another APOD Open Issues Why have Oberon and Umbriel apparently been inactive throughout their histories while Ariel and Titania have been at least partially resurfaced? The moon Titania - History, geography, structure, exploration The moon Titania Titania. © based on NASA images Titania is about half as large as Earth’s moon, roughly 1,000 miles or 1,600 kilometers in diameter. Titania orbits Uranus every 209 hours.

Titania, like many other outer planet moons, is tidally locked. This moon also rotates once per orbit, giving Titania a “day” of 209 hours. Titania orbits at almost zero degrees inclination from Uranus’ equator, which is remarkable given that Uranus essentially rotates on its side. History of Titania William Herschel. © National Portrait Gallery, London Titania was discovered in 1787. The name comes from the queen of the fairies in one of Shakespeare’s plays. Titania’s husband in the play is Oberon, which is the name given to another of Uranus’ moons by Titania discoverer William Herschel. Titania is the larger and closer of the two great Uranian moons. Uranus also has three more large moons and more than 20 small moons. Because of the discoverer’s penchant for naming Uranus’ moons for characters out of Shakespeare, later astronomers kept up the tradition, naming features on Titania and the other moons of Uranus. Most new moons and craters are named for characters out of Shakespeare’s comedies, while major features like grabens and flat planes are named for places out of the plays.

Titania is thought to have formed from the rocky material that coalesced around Uranus as the planet forms. This would make the moon about four and a half billion years old. However, its surface has few craters. Uranus’ moons. © NASA It is suspected that Titania suffered an endogenic event. The planet was warmed, melted and reformed its surface. This process left giant canyons as well. It is possible that this reforming occurred at the same time that Uranus was literally knocked onto its side. It is thought that Titania’s interior expanded at some point after its formation, causing the formation of giant cracks called scarps on its surface. The expansion of Titania’s interior cracked its frozen exterior. This may have occurred if it had a liquid water-ammonia ocean that later froze. This theory is supported by the few craters across these scarps, suggesting that they haven’t had much time geologically to be marred by many craters. Geography of Titania Titania has several major impact craters. Gertrude it is roughly three hundred kilometers across and two kilometers deep. Gertrude was named for a character out of one of Shakespeare’s plays.

Ursula is a crater about 140 kilometers across. Titania is marred by grabens, giant, raised parallel faults. Similar features can be found on Earth in places like Canyonlands National Park in the United States and African Great Rift Valley. The valleys between the grabens are called scarps. The largest graben on Titania is called Messina Chasma. Giant cracks called scarps on Titania’s surface. © NASA This 1,500 kilometer fault runs northwest to southeast. Belmont Chasma or “canyon” runs east on Titania and is about 260 kilometers long. It cuts through the crater Ursula. Rousillon Rupes or “scarp” is the name given to another, large scarp. Most of the scarps are named for places in Shakespeare’s plays. Many of the other named craters were given names from Shakespeare. There is Valeria, Mopsa, Lucetta, Marina, Phrynia, Iras, Bona, Adriana, Imogen and Calphurnia. Other craters have conventional British names like Katherine, Elinor and Jessica. If Titania has an atmosphere, it is miniscule.

Any atmosphere would comprise of carbon dioxide slowly replenished by exposure of frozen carbon dioxide to sunlight. If there is an atmosphere, it would be one billionth of the atmospheric pressure of Earth’s atmosphere. The surface of Titania hovers between sixty and ninety degrees Kelvin; this temperature is not very far above the point where molecular hydrogen freezes and becomes a solid. It is possible that Titania’s atmosphere is seasonal, only developing during the moon’s 42 year summer during Uranus’ 84 year long trip around the sun. This would mean that only the side of the moon in summer has an atmosphere, while the dark side of the moon’s atmosphere is frozen. Titania may have had a thicker atmosphere in its past, since Uranus’ magnetosphere would strip any gaseous particles from the moon’s surface. Inside Titania Uranus is extremely cold. While it has a magnetic field, this magnetic field seems to originate from a water-ammonia ice ocean around its solid core instead of a molten core. Uranus does not generate a significant tidal pull on Titania, nor does the planet generate heat that warms its moons. Titania doesn’t reflect much sun light since it is mostly comprised of rock and ice.

While it probably contains water ice, it is cold enough to contain frozen ammonia and carbon dioxide. It is likely that Titania has stratified internal layers. For example, Earth has a molten core, a semi-liquid mantle and a solid surface. Titania has experienced significant tidal forces in its past and could have had tidal heating or geothermal heating powered by Uranus’ magnetosphere. This would allow Titania’s original rock and ice mixture to warm, coalesce and reform. This would create a solid rock core, a mantle of ice mixed with ammonia and rock and a crust of ice. This remolding of the planet would explain the relatively young surface of the moon and how its graben formed. There may or may not be a liquid layer today between the icy surface and rocky core. If Titania had an underground ocean, it would have to have significant quantities of liquid ammonia to avoid freezing at the moon’s current, low temperatures. Internal structure of Titania. © NASA images Another possibility is that Titania had radioactive elements in the rocky material the coalesced to form the moon. The radioactive heating as the moon formed would help the core solidify while lighter elements migrated to the surface.

If the core was heated by radioactive decay, this ended within a few hundred million years of the moon forming. As the radioactive material settled in the core, the heating would cause Titania to expand. This would create cracks and fault lines on the frozen surface while helping smooth out any existing craters. Exploration of Titania Uranus’ moons have been studied using infrared reflectance photometry from Earth. M. J. Lebofsky and G. Rieke were pioneered this work in 1981. Voyager 1 was not able to pass by Uranus. Voyager 2 arrived at Uranus in 1986. That trip only revealed detailed pictures of 40% of the moon’s surface. There are several proposed missions to Uranus and its moons, but there are no missions planned by any space agency at this time. What do we know about Uranus' moons? Part 1 | The Planetary Society What do we know about Uranus' moons? Part 1 EDIT: Here's Part 2 . And here's a link to the transcript of my podcast .

While preparing for an upcoming 365 Days of Astronomy piece I did on the Voyager 2 Uranus encounter (look for that on Friday), I got an urge to dive in to the Voyager image archives and see what exactly we have here on Earth to base our understanding of the Uranian moons on. In recent years I've gotten used to the luxury of orbiters having repeated encounters with moons, with Galileo at Jupiter, Cassini at Saturn, and all the Mars orbiters that can look at Phobos and Deimos. But before we had these orbiters, there were just flyby missions, which had a very limited opportunity to survey the whole planetary systems. For Uranus and Neptune, the Voyager 2 flybys are it, in terms of moon imaging; nothing that we have on (or above) Earth can photograph the moons in high enough resolution to teach us much about what their surfaces look like. NASA / JPL Voyager 2 trajectory through the Uranus system Voyager 2 flew by Uranus on January 24, 1986.

The close encounter period of Voyager 2's flyby of Uranus lasted only about six hours around the spacecraft's closest approach on January 24, 1986 at 17:59 UTC, though observations took place over a 16-week period from November through February. The moons, being on the small side, were pretty much just dots to Voyager 2 until just two or three days out. Because the Uranian system is tipped sideways, the orbits of the moons appeared like a bull's eye to the approaching Voyager 2. So unlike the other giant planet encounters, where the trajectory could be selected to minimize the approach distance to several moons as Voyager 2 shot through the system more or less within the moons' orbital plane, at Uranus they had to pick ahead of time which moon Voyager 2 would fly closest to, a decision that really had more to do with where the spacecraft needed to shoot by Uranus in order to wind up with a course that would take it to Neptune. The optimal Uranus approach distance wound up being at about the distance of Miranda's orbit, so Miranda it was, even though it was the smallest of the five known moons and therefore likely the least interesting.

They lucked out -- Miranda turned out to be the most interesting! Voyager 2 got to within 26,000 kilometers of Miranda. As you can see in the diagram above right, it had nearly as close an encounter with Ariel, about 28,000 kilometers. Titania was farther away, and Oberon and Umbriel MUCH farther away. The brief encounter meant that there just wasn't much time to take many images of each place, so it is not at all hard to show you the entire catalog of Voyager images of each of the moons it flew by. Now, noodling around with raw image data is something that I do when I am overwhelmed by the demands of work and home life and need to go take a break -- it feels like I'm being productive, but it's really procrastination. So I haven't gotten completely through the image catalog; I've just done Ariel and Miranda to show you the best stuff, and Oberon to show you that there's still a lot to be learned about what the Uranian moons look like. Yes, that really is the best set of images we have from Oberon.

Every photo that you have ever seen of Miranda, Ariel, or Oberon was crafted from one or another subset of the images that you see below, processed in one way or another. NASA / JPL / PDS Rings Node / montage by Emily Lakdawalla Voyager 2's Miranda image catalog Miranda is the smallest of Uranus' major moons with a diameter of only 471 kilometers. Voyager 2 passed within 26,000 kilometers of it during its January 24, 1986 flyby, capturing a high-resolution mosaic covering the entire sunlit southern hemisphere and revealing its strange, contorted terrain. NASA / JPL / PDS Rings Node / montage by Emily Lakdawalla Voyager 2's Ariel image catalog Ariel is Uranus' fourth largest moon with a diameter of 1,158 kilometers. Voyager 2 passed relatively close to it on its January 24, 1986 flyby, acquiring a high-resolution mosaic that suffers from some motion blur.

NASA / JPL / PDS Rings Node / montage by Emily Lakdawalla Voyager 2's Oberon image catalog Oberon is Uranus' second largest moon with a diameter of 1,522 kilometers. It is the farthest major moon from Uranus, so Voyager 2 only got a distant look during its January 24, 1986 flyby. Compared to what we have from Galileo and Cassini at Jupiter and Saturn, these images are pretty gnarly. I have enhanced the contrast to make details a little easier to see, but you can still see a gray background to a lot of the photos. That background is space, and it should be black; the grayness means that there's a lot of "dark current" within the Voyager imaging system, and the fact that its color isn't constant gray but is a little speckly tells you that there's noise in the images too, which reduces their quality. It's hard work to make beautiful images of these. Of course, that makes it exactly the kind of data set that Ted Stryk likes to play with; here are his versions of the image catalogs.

The images are grayscale, but they include much of the data shown above: he stacked images that were taken at nearly the same time, a process that helps to reduce the effects of random noise and increase the quality of the details in each image. NASA / JPL / Ted Stryk Voyager 2's images of Uranian moons From top to bottom: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon. And here's the moons in color -- Ted used the Voyager 2 data for color, except for Puck, which Voyager 2 never imaged in color. In fact there is only one image in existence of poor little Puck. NASA / JPL / Ted Stryk Colors and sizes of Uranus' moons The six largest moons of Uranus, to scale with each other, showing their relative colors and brightnesses. From left to right: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon. Color data is from Voyager 2, except for tiny Puck, whose color is derived from Hubble data. OK, I've noodled around enough that now I'm even more behind than I was when I started playing with the Voyager data. Which is what always happens.

But I've had a satisfying day! Oberon, moon of Uranus - The Solar System on Sea and Sky Voyager 2 close-up of Oberon (NASA/NSSDC) King of the Fairies Oberon [OH buh ron] is the outermost of Uranus' moons and is the second largest. It was named after the King of the Fairies and husband of Titania in Shakespeare's Midsummer-Night's Dream. Oberon was discovered in 1787 by the British astronomer, Sir William Herschel, who also discovered Uranus. Most of what we now know about this moon was discovered by Voyager 2 in 1986. Mysterious Dark Craters Oberon is very similar to Umbriel in composition, although Oberon is about 35% larger. As with all of Uranus' moons, it is believed to be composed of about half water ice and half rocky material. The surface of Oberon is heavily cratered. The lack of other surface features indicates that it has probably been stable since its formation. An unidentified substance covers the floors of many of Oberon's craters. Astronomers are not yet sure where this substance originates.

One theory suggests that it could be "dirty water" that upwelled into the crater after impact. Features of Oberon The most notable features of Oberon are its craters. These craters are more numerous and much larger than those on Ariel and Titania. Some of these craters exhibit bright rays of ejecta material similar to those on Jupiter's moon, Callisto. Several images of Oberon show a lone mountain peak rising 4 miles (6 km) above the surface. In the southern hemisphere, large faults can be seen crossing the surface. This may be evidence of some type of geologic activity early in the moon's history. Oberon has no detectable atmosphere and no magnetic field. Voyager - Uranus' Moons From left, in order of increasing distance from the planet, they are Miranda, Ariel, Umbriel, Titania and Oberon. (Click on the image for a larger view) Moons Voyager 2 obtained clear, high-resolution images of each of the five large moons of Uranus known before the encounter: Miranda, Ariel, Umbriel, Titania and Oberon.

The two largest, Titania and Oberon, are about 1,600 kilometers (1,000 miles) in diameter, roughly half the size of Earth's Moon. The smallest, Miranda, is only 500 kilometers (300 miles) across, or just one-seventh the lunar size. The 10 new moons discovered by Voyager bring the total number of known Uranian satellites to 15. The largest of the newly detected moons, named Puck, is about 150 kilometers (about 90 miles) in diameter, or larger than most asteroids. Preliminary analysis shows that the five large moons are ice-rock conglomerates like the satellites of Saturn. The large Uranian moons appear, in fact, to be about 50 percent water ice, 20 percent carbon- and nitrogen-based materials, and 30 percent rock. Their surfaces, almost uniformly dark gray incolor, display varying degrees of geologic history. Very ancient, heavily cratered surfaces are apparent on some of the moons, while others show strong evidence of internal geologic activity.

Titania, for example, is marked by huge fault systems and canyons that indicate some degree of geologic activity in its history. These features may be the result of tectonic movement in its crust. Ariel has the brightest and possibly the geologically youngest surface in the Uranian moon system. It is largely devoid of craters greater than about 50 kilometers (30 miles) in diameter. This indicates that low-velocity material within the Uranian system itself peppered the surface, helping to obliterate larger, older craters. Ariel also appears to have undergone a period of even more intense activity leading to many fault valleys and what appear to be extensive flows of icy material. Where many of the larger valleys intersect, their surfaces are smooth; this could indicate that the valley floors have been covered with younger icy flows. Umbriel is ancient and dark, apparently having undergone little geologic activity. Large craters pockmark its surface. The darkness of Umbriel's surface may be due to a coating of dust and small debris somehow created near and confined to the vicinity of that moon's orbit.

The outermost of the pre-Voyager moons, Oberon, also has an old, heavily cratered surface with little evidence of internal activity other than some unknown dark material apparently covering the floors of many craters. Miranda , innermost of the five large moons, is one of the strangest bodies yet observed in the solar system. Voyager images, which showed some areas of the moon at resolutions of a kilometer or less, consists of huge fault canyons as deep as 20 kilometers (12 miles), terraced layers and a mixture of old and young surfaces. The younger regions may have been produced by incomplete differentiation of the moon, a process in which upwelling of lighter material surfaced in limited areas. Alternatively, Miranda may be a reaggregation of material from an earlier time when the moon was fractured into pieces by a violent impact. Given Miranda's small size and low temperature (-335 degrees Fahrenheit or -187 Celsius), the degree and diversity of the tectonic activity on this moon has surprised scientists. It is believed that an additional heat source such as tidal heating caused by the gravitational tug of Uranus must have been involved.

In addition, some means must have mobilized the flow of icy material at low temperatures. This page was last updated June 11, 2014

Question: Titania is the largest moon of Uranus by diameter. Which is the second largest?
Answer: OBERON